The present invention relates to an improved magnetic recording material and a method for producing the same, and more specifically relates to production of a magnetic recording material in which information is accumulated in magnetic substance packed in micro pores extending in the thickness direction of the material.
Thickness directional magnetic recording of this type is known to be suited for high density recording in which a great deal of information (bits) is stored in a very small area of a magnetic recording medium of a memory.
One example of the production of such a high density magnetic recording material is disclosed in U.S. Pat. No. 4,109,287. In the process of this proposed system, a layer having a great number of micro pores, which extend in the thickness direction of the layer, is formed on the surface of a substrate containing predominant amount of aluminum by anodic oxidation (the first electrolytic treatment) and magnetic substance is packed in the micro pores by electrolytic deposition (the second electrolytic treatment).
In the construction of the magnetic recording material produced by this proposed system, the diameter of the micro pores in the anodic oxide layer varies generally within a range from 10 to 40 nm (nanometers). When the magnetic substance is packed in the micro pores of such a small diameter, the resultant magnetic recording material exhibit a high coercive force in the thickness direction which amounts to 120,000 A/m or higher. When recording and erasing of information are performed using a magnetic recording material of such a high coercive force with a narrow head gap, magnetic saturation takes place at the tip of the magnetic head and, as a consequence, the magnetic recording material of the above-described earlier proposal is quite unsuited for high density recording. Even when the coercive force of the resultant magnetic material is occasionally below 120,000 A/m, the easily magnetizable direction is almost parallel to the surface of the magnetic recording material and, therefore, it is next to impossible to accumulate information in the axial direction of the magnetic substance packed in the micro pores. Further, even when the easily magnetizable direction is somewhat normal to the surface of the magnetic recording material, the resultant residual magnetic flux density is lower than 0.03T which value disenables generation of sufficient reproduction output. These factors all concur to make the magnetic recording material of the earlier proposal quite unsuited for use in high density magnetic recording.
In addition to the foregoing, the accumulating capacity of information of the magnetic recording material is significantly swayed by the rate of packing of the magnetic substance in the micro pores. As a result of a series of confirmation tests conducted by the inventor of the present invention, it was confirmed that the process of the abovedescribed earlier proposal cannot always assure full packing of the magnetic substance in the micro pores.